Last time it happened to me I was riding to an area I had never ridden before, looking for a specific street. The road I was on roughly followed the river that was just east of it. Between the road and the river was a park area that had a MUP going through it. I would have been willing to ride on the MUP, except for the fact that I was trying to find the correct street and the MUP didn't exactly have signs telling you which streets were intersecting the road running parallel to the MUP. Thus in about a 1-1.5 mile stretch on this road I got flipped off once, yelled at to "get on the bike path" about 4-5 times, and had people lay on the horn as they passed more than that. It was great.